Interior permanent magnet (IPM) machines are favored for fuel cell and hybrid electric vehicle operations due to their desirable characteristics—good torque density, high overall efficiency, and relatively constant power range, etc. The rotor field in a permanent magnet machine is obtained by virtue of its structure, unlike other machines such as induction, switched or synchronous reluctance machines, in which the field is generated by a stator current supplied by a source. As a result, permanent magnet machines exhibit superior efficiency as compared to other such machines.
In an IPM machine, one or more rotor barriers—including permanent magnets and/or air gaps—are often added. These rotor layers act as barriers to the permanent magnet field of the lower primary magnet layer, reducing the air-gap magnet flux, and lowering the machine back EMF and losses induced by the permanent magnet field.
Traditional IPM rotors are unsatisfactory in a number of respects. For example, the cavities or slots provided within the rotor for accepting the inserted magnets often have a complicated shape, and typically require formation of magnets with trapezoidal and/or more complicated geometries. Fabrication of such magnets is time consuming, costly, and requires tight tolerances. Furthermore, the magnet material used for forming such magnets (e.g., NdFeB) is significantly more expensive than standard magnet material (e.g., ferrite materials).
Accordingly, it is desirable to provide improved IPM rotor designs that are manufacturable, inexpensive, and which maintain suitable magnetic characteristics. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.